Renal Physiology Lecture 2: Formation of Concentrated Urine

Question 1

What helps to maintain osmolarity?

Answer 1

The arrangement of the loop of henle and the surrounding vessel

Question 2

Urine concentration process in the loop of Henle

Answer 2

1. Solute and water are reabsorbed in the proximal tubule
2. filtrate enters the descending limb
3. Isosmotic fluid leaving the proximal tubule becomes progressively more concentrated in the descending limb as only water is reabsorbed (more permeable to water than the solute)
4. Removal of solute in the thick ascending limb creates hyposmotic fluid (permeable to solute but not water)
5. Tubular fluid becomes more dilute as it ascends.
6. Permeability to water and solutes in the distal tubule and collecting duct is regulated by hormones → vasopressin
7. Final urine osmolarity depends on reabsprotion in the collecting duct

Question 3

Osmolarity

Answer 3

Osmolarity is a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)

Question 4

Hyposmotic vs. hyperosmotic

Answer 4

the solution with the higher osmolarity is said to be hyperosmotic to the other, and the solution with lower osmolarity is said to be hypoosmotic. If two solutions have the same osmolarity, they are said to be isoosmotic.

Question 5

What part of the loop of Henle does vasopressin work?

Answer 5

distal tubule

• absent not permeable to water so solute reabsorbed but water cant follow and have concentrated urine
• presence makes it permeable to water so it is reabsorbed with solute and urine is dilute

Question 6

What is the vasa recta?

Answer 6

Vasa recta is the minute vessel of the peritubular network which runs parallel to the loop of Henle.

• the straight arterioles, and the straight venules of the kidney, – a series of blood vessels in the blood supply of the kidney that enter the medulla as the straight arterioles, and leave the medulla to ascend to the cortex as the straight venules.

Question 7

Function of the vasa recta

Answer 7

It maintains the concentration gradient in the medullary interstitium and helps to maintain the osmolarity of blood.

Question 8

How does fluid flow in the vasa recta?

Answer 8

Countercurrent exchange

• Fluid flows in the opposite direction to that of the tubular fluid

Question 9

How does the counter current exchange in the vasa recta work?

Answer 9

• Filtrate entering the descending limb becomes progressively more concentrated as it loses water
• blood in the vasa recta removes water leaving the loop of Henle → moving in the opposite direction
• The ascending limb pumps out Na, K, and Cl, and filtrate becomes hyposmotic

Question 10

osmolarity leaving the loop of Henle

Answer 10